Summary

Optokinetic nystagmus cannot regularly be elicited under scotopic conditions if only one eye is stimulated by rotating an optokinetic drum at a certain speed. Exposing both eyes to the same or a much weaker optokinetic stimulus evokes a marked optokinetic reaction. The relatively small differences between monocular and binocular thresholds of light perception and between critical flicker fusion frequencies cannot entirely explain this phenomenon. It must be assumed that in reduced illumination also other factors, such as variations in sensation time and/or impaired recognition of movement, are involved.